Abstract: Safinamide mesylate is mainly used in the treatment of Parkinson's disease. A liquid chromatography-mass spectrometry (LC-MS) method was developed for the determination of genotoxic impurities ((S)-4-((1-amino-1-oxopropane-2-methyl)amino)methyl)benzoate) in safinamide mesylate. The sample was dissolved in methanol, separated by YMC-Triart C18 column (4.6mm×100 mm, 3μm), eluted with 0.1 % formic acid in water and 0.1 % formic acid in methanol gradient, and quantified by positive ion scanning in multiple reaction monitoring (MRM) mode. The method has good specificity, and the target compound has a good linear relationship in the concentration range of 1.53-30.54 ng/mL. Standard recovery rate was 98.5%～99.90% with relative standard deviations of 0.83%～2.10%. The linear response range was between 1.53～30.54 ng/mL (R² >0.99). The results showed that the method was sensitive, accurate, reliable and suitable for screening of genotoxic impurities ((S) - 4 - ((1-amino-1-oxopropane- 2-methyl) amino) methyl) in safinamide mesylate.